Toughened glass

ABSTRACT

Toughened glass of thickness in the range 0.8 mm to 3.5 mm is obtained by quenching in a two-component liquid medium, and has a modulus of rupture of from 14 X 103 p.s.i. and, upon destruction by sharp impact fracture, shatters into from 8 to 100 fragments per cm2 of the glass.

United States Patent [1 1 Wartenberg [4 1 Feb. 19, 1974 TOUGHENED GLASS[76] Inventor: Erwin W. Wartenberg,

Brunnenwiesen 6, Riedenberg, Stuttgart, Germany [22] Filed: Nov. 30,1971 [21] Appl. No.: 203,428

Related US. Application Data [60] Division of Ser. No. 74,897, Sept. 23,1970, Pat. No. 3,653,866, and a continuation-in-part of Ser. No.

692,778, Dec. 22, 1967, abandoned.

[30] Foreign Application Priority Data Dec. 28, 1966 Germany W43078 [52]US. Cl. 161/1, 161/165 [51] Int. Cl C031) 27/00 [58] Field of Search161/164-166, 1;

[56] References Cited UNITED STATES PATENTS 1,976,915 10/1934 Black..161/411X 3,107,196 10/1963 Acloque 161/164 3,186,816 6/1965Wartenberg.. 65/116 3,592,726 7/1971 Blizard 161/166 X 3,595,725 7/1971Coen 65/114 X 2,285,595 6/1942 Littleton et al.. 65/116 2,198,739 4/1940Phillips 65/116 3,271,207 9/1966 Davis 65/116 X Primary ExaminerCharlesE. Van Horn Attorney, Agent, or Firm-John P. Snyder [5 7] ABSTRACTToughened glass of thickness in the range 0.8 mm to 3.5 mm is obtainedby quenching in a two-component liquid medium, and has a modulus ofrupture of from 14 X 10 p.s.i. and, upon destruction by sharp impactfracture, shatters into from 8 to 100 fragments per cm of the glass.

12 Claims, 3 Drawing Figures PATENTEB FEB 1 9 I974 sum 2 or 2 263 col/g:55; E mo 29.25.2528

NUMBER OF PARTICLES PER 0M2 FIG. 2

TOUGHENED GLASS CROSS REFERENCE TO RELATED APPLICATIONS This applicationis a division of co-pending application Ser. No. 74,897, filed Sept. 23,1970 now US. Pat. No. 3,653,866 and is a continuation-in-part of priorcopending application Ser. No. 692,778, filed Dec. 22, 1967 and nowabandoned.

BACKGROUND OF THE INVENTION The present invention relates to toughenedglass produced by quenching a hot glass body in a quenching liquid.

It is known to increase the mechanical strength of glass by a tougheningprocess. Such toughening is carried out by first heating the glass andthen uniformly and suddenly cooling the heated glass, i.e., byquenching. Gases or liquids may be used as quenching agents. Toughenedglasses find practical application, for example as glass windows formotor vehicles, due to the fact that toughened glass has increasedstrength and, furthermore, upon being subjected to stress the properlytoughened glass sheet will fragment into a great number of relativelysmall particles which do not have sharp, and therefore dangerous, edges.

Known liquid quenching methods are effective for toughening glass sheetshaving a thickness of at least about. 3.4 mm, to improve the mechanicalstrength of the glass which, upon severe impact, breaks into manyrelatively small and harmless particles. Control of particle count isessential in the manufacture of safety glass for motor vehicles.

Usually, safety glass used in motor vehicles has a thickness of betweenabout 5 mm and 6 mm. However, it is becoming more and more desirable toreduce the thickness of automobile glass, particularly in view of thelarger glass area which is used in modern automobiles. Thus for economicas well as for structural reasons it has become important to reduce thethickness of the glass used as windows and windscreens in motorvehicles.

It has also been found that this safety-glass because ofits highelasticity diminishes greatly the risk of severe skull injuries on headimpact.

Many attempts have been made to produce extremely thin glasses, which interms of their mechanical strength, and fracture characteristics andelasticity upon severe impact, are suitable for use in motor vehicles.It has been found desirable to reduce the thickness of automobilewindows to between about 1.6 mm and 2.5 mm. However, it has not beenpossible hitherto to toughen glass sheets of such small thickness byconventional methods, in such a manner that the toughened glass willcomply with official safety requirements and will possess the mechanicalstrength desirable for automobile windows, windscreens and the like.

Recently chemical toughening methods have been developed for producingglass sheets having a thickness of between about 2.0 mm and 2.5 mm whichsheets have a high degree of mechanical strength and form the desiredlarge number of small particles upon being disintegrated by mechanicalforce. These methods are based on the principle of ion exchange.Although the glass sheets produced by this method are thinner and havehigher modulus of rupture than glass which was toughened by theconventional quenching method, the

ion exchange method has the great disadvantage that it cannot be usedfor toughening glass sheets or ordinary soda-lime-silica composition.Alumino-silicate glass must be used as an initial material in theion-exchange process, in order to produce residual compressive stress atthe surface of the glass by exchange of sodium for potassium or lithiumions. Toughening by ion exchange cannot be achieved with ordinary sheetglass because the chemical composition of ordinary sheet glass isunsuitable for ion exchange processes.

It is an object of the present invention to provide a process for thetoughening of a wide range of glasses, irrespective of theircomposition, including ordinary sheet glass and, furthermore, to toughensuch glass sheets which are relatively thin. By the method of thepresent invention it is possible to toughen glass sheets whose thicknessis considerably less than 3.5 mm and to obtain the same mechanicalstrength as is obtainable in alumino-silicate glasses by the ionexchange methods. Glass sheets having a thickness of only about 0.8 mmwhen toughened in accordance with the present invention, will fragment,when shattered, into small and relatively harmless glass particles.

Toughened glass produced by the method of the present invention isparticularly suitable as single sheet safety glass in motor vehicles.The mechanical strength of the toughened glass is about 8 times as highas the mechanical strength of untoughened glass and about three timesthe mechanical strength which is obtained by subjecting similar glass toa conventional quenching method.

The high degree of mechanical strength of the glass, particularly ofglass sheets, is achieved by quenching the glass in a chilling liquid insuch a manner that the glass will be cooled much faster than has beenpossible hitherto. The speed of cooling exceeds that which could beobtained by using pure water as a chilling liquid, although it has beenassumed that pure water rep resents the fastest and most effectivechilling liquid.

Many attempts have been made to toughen glass by quenching in water;however, these attempts were not successful because quenching of heatedglass in water caused cracking of the glass or at least considerabledamage to the glass surface so that water-quenched glasses had to bediscarded.

US. Pat. No. 3,186,816 and German Pat. No. 1,034,333 disclose processesaccording to which heated glasses are quenched in a liquid and theenergy required for vaporization of the liquid causes quick cooling ofthe glass. The liquid which is used for quenching is maintained by asuccession of hot glasses at a temperature in the vicinity of andpreferably slightly below, its boiling point.

It has been found possible by three prior methods to toughen glasses ofthickness at least 3.5 mm and to obtain thereby glasses which fragmentinto a great number of relatively small and harmless particles. However,it has not been possible to toughen glasses less than about 3.5 mmthick, because liquids having the required high heat of vaporization,when used for quenching relatively thin glasses, cause immediatedestruction of the glass. Furthermore, within a range of heat ofvaporization between about and calories per gram, it was not possible toproduce a substantial reduction of the length of the quenching period ora substantial increase in the speed of cooling of the glass andconcomitant therewith an increase in the mechanical strength of thetoughened glass.

The methods of the two patents mentioned above require the formation ofa gas layer or vapor sleeve around the hot glass in order to obtainfaster quenching without destruction of the glass. The patents describespecial ways of enhancing the formation of such vapor sleeve.Surprisingly, it now has been found that, notwithstanding the fact thatthe cooling of the glass is caused by vaporization of quenching liquid,the formation of a continuous gas or vapor layer along the glass surfaceand the maintenance of such gas or vapor layer for a certain period oftime is undesirable when toughening thin glass, because extremely quickcooling which is the decisive requirement for obtaining the desired highdegree of toughening of thin glasses, is prevented by the formation ofsuch vapor layer.

Consequently, the present invention proposes to maintain throughout thequenching process direct contact between hot glass and quenching liquid,without the production of an interposed vapor layer.

SUMMARY OF THE INVENTION Toughened glass, in particular a toughened thinsheet of soda-lime-silica glass, is produced by quenching the hot glassin a quenching bath which consists essentially of a major proportion ofa liquid which is inert relative to the glass and a minor proportion ofa low boiling point additive.

Glass of thickness in the range 0.8 mm to 3.5 mm when so toughened has amodulus of rupture of from 14 X psi. to 56 X 10 psi. and, upondestruction by sharp impact fracture, a fragmentation number of from 8fragments per cm to 100 fragments per cm.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphic representation ofthe relationship with respect to various quenching liquids andconcentrations between heat of vaporization and the number of glassparticles formed upon destructive impact;

FIG. 2 is a graphic representation of the relationship betweenconcentration of two lower boiling point liquids, and the number ofglass particles formed upon destructive impact; and

FIG. 3 is a graphic illustration of the relationship between the numberof glass particles formed upon destructive impact and the concentrationof a low boiling point liquid in the chilling liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the presentinvention, sudden cooling of the glass body is achieved due tovaporization of a low boiling point cooling liquid in direct contactwith the surface of the hot glass body.

This is achieved by using as a liquid quenching medium, a chillingliquid which is a mixture of carrying liquid having a relatively highboiling point, but which is below the temperature of the heated glassbody, and a second liquid which has a lower boiling point than thecarrying liquid in an amount of up to about 4% of the weight of thechilling liquid thus formed. The low boiling point liquid must have aboiling point and heat of vaporization such that it will quicklyevaporate when it is in contact with the hot glass. The low boilingpoint liquid is chosen in dependence on the degree of tougheningrequired, and so that there is a relativelylarge difference, of at least100 C, between the boiling point of the low boiling point liquid and theincipient boiling point of the carrying liquid, which is at least 200 C.The nature of the low boiling point liquid is such that uponvaporization it will not have any destructive effect on the surface ofthe hot glass body.

Due to the relatively small proportion of low boiling point liquid whichis incorporated in the chilling liquid, the low boiling point liquidwill be vaporized in contact with the glass surface but will not becapable of fonning thereon a coherent gas or vapor layer on the glasssurface.

The method of the present invention may be used to quench glasses of anycomposition, for instance, sodium-potassium glass or, generally, alltypes of alkali metal alkaline earth metal silicate glasses, e.g.sodalime-silica glass. The method may be used for the quenching of alltypes of plate glass and window glass as well as for special glassessuch as bore-silicate glasses or lead-silicate glasses. 7

In an earlier liquid quenching method a piece of plate glass which hasbeen heated nearly to its softening point, for example to about 630 C,and which is 1.8 mm thick, and has an expansion coefficient of 90 X l0 Cwas quenched in pure boiling carbontetrachloride and a continuousgaseous phase was formed on the surfae of the cooling glass body andpersisted for about 40 seconds. Glass which has been quenched in thismanner has a mechanical strength which is about twice that of similarbut untoughened glass. However, upon being subjected to destructiveimpact, the glass thus quenched will not disintegrate into a greatnumber of relatively small and harmless particles.

The formation of a continuous vapor layer on the glass surface isprevented according to the present invention by incorporating in acarrying liquid whose incipient boiling point is at least 200 C, arelatively small proportion of a low boiling point liquid whose boilingpoint is at least 100 C below the boiling point of the carrying liquid.The chilling liquid thus formed is used as a quenching bath, preferablyat a temperature which is in the vincinity of, usually slightly below,the boiling point of the low boiling point liquid. Because the boilingpoint of the carrying liquid is at least 100 C higher than the boilingpoint of the low boiling point liquid, essentially only the low boilingpoint liquid is vaporized during the quenching of the hot glass. Thepresence in the chilling liquid of at least about 96% by weight of thehigher boiling point carrying liquid, prevents the formation of acontinuous gas or vapor layer even though the low boiling point liquidis being varporized and, consequently the cooling and quenching of theglass 7 takes place immediately the hot glass enters the liquid,

by the vaporization of low boiling point liquid in direct contact withthe hot glass surface. The entire heat required for the vaporization ofthe contacting low boiling point liquid is withdrawn rapidly from theglass and thereby very quick cooling is achieved during whichessentially only low boiling point liquid is vaporized.

For obtaining the desired high degree of toughening, it is importantthat cooling of the glass from a temperature just below the softeningpoint of the glass, i.e., from the temperature at which the hot glass isexposed to quenching, for example 630 C, down to a temperature below thestrain point of the glass,-e.g. about 350 C is carried out as quickly aspossible. Such very quick cooling is achieved according to the presentinvention I by the vaporization of the low boiling point liquid in diofthe quenching bath is of little consequence in deter- In these tests 4.5grams of methanol were added to 5 litres of the mineral oil to give aconcentration of 0.1% by weight; and 22.5 grams of methanol were addedto 5 litres of the mineral oil to give a concentramining the finaldegree of toughening of the glass. 5 ti f 05% b i ht Refemhg now to thedrawmg P 1 nustrates the These results are illustrated graphically inFIGS. 2 relationship between heat of vaporization and the fragand 3, anda 2 Shows that when between 0.2% and mentation number for carbontetrachloride CCl ben- 1% by weight of Carbon tetrachloride is added tothe Zehe CGHB; ternary butanol (CH3)3COH; ethanP] mineral oil thechilling liquid thus formed is heated to z sq aQ p y as low h betweenabout 80 C and 100 C and used at that temlhg P hquld m a hhhel'al Shellwhose perature as quenching bath for toughening glass 1.8 Cipieht hoihhgP is about 3000 The lefthahd mm thick, by heating the glass inconventional manner curve represents a concentration of 0.3% by weightand and the quenching the glass in the bath toughened right-hand curve acohcehh'ahoh of 1% y Welghtglass is produced which, when subjected todestructive It is evident from the curves of FIG. 1 that withincreasimpact, h a f t ti number f between about lhg heat ofvaporization of the low boiling Poiht liquid, 15 and 45 particles persquare centimeter and has a the number of particles formed uponfragmentation modulus of rupture of between 14 X 10 p.s.i. and 28 andthus the degree of toughening of the glass will in- X 10 psi, 01- evenhigher, up to 42 X 10 p.s.i. crease' A s is evident from the curves ofFlGfZ the fragmen- The marked Points on the curves of 1 are tationnumber and thus the tensile strength of the glass lected from testscarried out under similar conditions increases with increasingconcentration f low boiling with the Same high boiling point liquidShell point liquid. The right-hand curve of FIG. 2 shows that which hasa density of 091, Viscosity of 0st at substantially the same trend isindicated when metha- C, and flash point of 290 C. The incipient boilingpoint i d of this 011 is about 300 c.

FIG. 3 IS a curve, based on some of the results tabu- Table glves {esuusobtamed usmg K lated in Table I, in which fragmentation number on de- "f(bollmg pomt 76 C) as the low bollmg pomt structive impact is plottedagainst the concentration of carbon tetrachloride in the mineral oil. Itis evident A glass Sheet Whose Foemclem of expanslon 90 X from thiscurve that when the concentration of carbon 1on7 and dlmhnslons 100 X100 X L8 mm tetrachloride is about 1.5% by weight there is onlyfurheated an electric furnace to abfmt C ther slight increase in thedegree of toughening of the mediate)! thereafter was immersed aquehchlhg bath glass for a considerable increase in the concentrationlocated below the furnace. The quenching bath of the f b n hl fidchilling liquid was constituted by a mixture of 5 litres Table I and Fla3 sheW the1t the eh of the mineral oil with several grams of carbontetrame of the glass reaeheS a maximum represented by a chloride 9 gramsofcarbon'titrachloflde equwa' fragmentation number of about 55 particlesper cm', lent to 02% by we'ght of the chlnmg hqu'd; 'f when theconcentration of carbon tetrachloride is of carbon tetrachloride isequivalent to 0.5% by weight about 24% to 3% by weight Thereafter es theeeneen of the chhhhghquld; and 45 grams of carbon f f l tration isincreased the degree of toughening gradually s qu t g ZZ hXfFlF h Q h fi h g falls, and when the concentration is increased to above e q en gbath was maintained at 1W and 4% by weight a pronounced reduction in thestrength the hot glass sheet upon immersion, was cooled within f htoughened glass i b v d, F rth it h about 6 Seconds to a temper ure of bu 0 C- e been found that too great a concentration of the low resultsachieved with different concentrations of carboiling point liquid, above4% by weight, may result in bon tetrachloride were as follows: theproduction of surface defects in the glass during TABLE I a ccl, weight0.1 0.2 0.5 0.4 0.5 0.6 1.0 1.8 2.4 4.0 4.3

[Fraifnefiiifitin s 14 27 28 39 46 e0 67 Number Modulus of 30 37 39.541.2 42 44 45 47.5 48.5 47.6 47 {Rupture (XIOI P- JJ The process wasrepeated under the same conditions quenching, e.g. the formation ofgrooves and hairline with the mineral oil Shell 0.3.3 as carrying liquidcracks in the glass surface. and with methanol CI-I,OH (boiling point68C) as the m low boiling point liquid. The results obtained were as.Genlarany m carrymg. the ll l hqulds follows: Wlth hlgl'l heat ofvaporizatio and boiling points high relative to that of the low boilingpoint liquid, and pref- TABLE II erably above 200 C and up to 400 C andmore, are suitable for use as the carrying liquid, provided that thecihoii 0.1 0.2 0.4 0.5 0.6 1.0 liquids employed do not have chemicaleffects on the Fm t 32 so 60 64 62 72 glass surface. The carrying liquidmay be an organic or ssage, an inorganic liquid.

Modulus or 33 43 43 5| 505 56 Suitable carrying liquids are listed belowby way of {Ru qire x10= example, with their boiling points in "C whereappropri- ..P::| ate:

Vegetable and animal fats oils and waxes including:

rape seed O1l whale oil palm oil palm wax shellac wax hydrogenatedcastor oil beeswax paraffin wax vfl 300C dodecane 216 tridccane 243tetradccane 253 pantadecane 270 hexadecane 287 octadecane 305 Eicosane343 naphthalene 210 l-allyl-naphthalene 256 l-chloro-naphthalenc 2632-chloro-naphthalene 256 1-(chloro-methyl)-naphtha1ene 2911,2-dichloro-naphthalene 295 1,3-dichloro-naphthalene 2911,7-dichlor-naphthalcne 285 2,3-dimethyl naphthalene 2651,6-dimethyl-4-isopropyl naphthalene 291 lethoxy naphthalene 280 l.2,3,4tetra hydronaphthalene (tetraline) 207 Z-acetyl-l-hydroxy naphthalene325 l-chloro-5-nitro-naphthalene 360 octachloronaphthalene 440 6-acetyltetraline 289 l-tctralane 255 diphenyl 255 O-tcrphcnyl 332 m-terphenyl365 diamyI-benzene 260-280 triamyl benzene 300-320 tetraamyl benzene320350 furfural butyrate 213 trichlorobenzene 210 orthophosphoric acid213 tributyl phosphoric 289 triisobutyl phosphoric ester 264 triphenylphosphoric ester 245 tripropyl phosphoric ester 252tris(3,S-dimethyl-phenyl) phosphoric ester 290 tri (2-to1yl) phosphoricester 410 l-hexadecyne 284 hexadecyl ester 360 l-hexadecanol 344hexadecanoic methyl ester 415 glycerol tripalmitate 310 stearin 300phenyl stearate 267 oleic acid 286 stearic acid 358 oleonitrile 330l-octadecyne 313 Anthracene 355 9,10-dihydroanthracene 3139,10-dihydro-9-ethyl anthracene 3Z0 9-phenyl anthracene 417 A very widechoice of liquids as carrying liquids is thus possible, as exemplifiedabove by such liquids as mineral oils and waxes, compounds withcondensed at which the quenching bath is to be used, so that the bathtemperature is well below the boiling point of the carrying liquid.

is of relatively little importance in determining the speed of coolingof the glass and the degree of toughening which is achieved by thequenching of the glass,

since the main heat transfer from the glass is achieved by thevaporization of the low boiling point liquid which forms only a smallproportion of the chilling liquid.

I it will be seen, as illustrated in FIG. 1, that -by iising the samefirst carrying liquid in combination with equal proportions of variouslow boiling point liquids, the speed of cooling of the glass and therebythe number of particles per square centimeter which are formed uponfragmentation and the mechanical strength of the glass, increases withincreasing heat of vaporization of the low boiling point liquid. Thisshows that the rapid cooling of the glass is actualy achieved by thevaporization of the low boiling point liquid.

It is advantageous For producing highly toughened glass to choose lowerboiling as well as higher boiling liquidswhichhayearelatively high heatof vaporzation.

Results of tests carried out with some other low boiling point liquidswill now be indicated in Tables 111 to VII.

TABLE III Monochlorobenzene C H Cl (boiling point 132 C) was mixed withthe same mineral oil Shell 0.8.3.

The glass was heated to about 720 C and the quenching bath was at C.

I 0.5 0.6 0.8 1.0 Fragmentation Number 19 20 35 30 TABLE IV V" V "mEthanol C H OH (Boiling point 77.6 C) was mixed with Shell Q.B.3 oil andthe quenching bath was maintained at 100 C.

- c,H .-,oH weight 0.2 0.4 0.5 1.0

Fragmentation Number 53 63 66 68 TABLE V I h H v Chloroform CHCl(Boiling point 61 C) was mixed :with Shell Q.B.3 oil and the quenchingbath was maintained at 100 C.

'CHCI; weight 0.7 1.0 1.5 2

{Fragmentation Number 30 40 S4 60 TABLE V] Benzene C 11 (Boiling point80 C) was mixed with Shell Q.B.3 oil and the quenching bath wasmaintained at 80 C.

CH weight 0.2 0.3 0.5 [.0

{Fragmentation Number 21 20 46 52 TABLE VI] Trichloroethylene C 11 C1(Boiling point 86 C) was mixed with Shell Q.B.3 oil and the quenchingbath was maintained at 100 C.

C,H cl, weight 0.4 1.0 125 2 {Fragmentation Number 14 35 52 56 When lowboiling point liquids are used which contain OH groups, and have a highheat of vaporization, e.g. CH OH, C H OH, toughened glasses are obtainedwhich may have a modulus of rupture of about 42,000 p.s.i. and thus arefar superior to similar glasses which were quenched in conventionalmanner and thereby obtained a modulus of rupture of about 14,000 p.s.i.The values for modulus of rupture which are achieved according to thepresent invention are of the same magnitude as those of glasses whichhad been toughened by the ion exchange method. The number of particlesinto which toughened glasses will disintegrate upon destructive impactmay be more than l/cm even if the glass was of a thickness of only 1.5mm. The mechanical strength of such very thin glasses which aretoughened by the method of the present invention makes it possible tobend these glasses easily so that the glass originally may be formed asa flat sheet and subsequently may be installed in curved rigid framesbecause it is able to adjust itself to a certain degree of curvature.The method of the present invention may also be used for tougheninghollow or curved glass. Due to the high rate of cooling the method isparticularly suitable for glass having a relatively small coefficient ofexpansion. Thus, good results are obtained with glasses havingcoefficients of expansion of between X C and 120 X 10 C and preferablybetween 30 X 10- C and 90 X 10' C".

As pointed out above, the proportion of low boiling point liquid in thechilling liquid should not exceed about 4% by weight of the chillingliquid and generally will be between about 0.1% and 4% by weight,preferably between 0.5% and 2%.

It is a significant advantage of the present invention that by changingthe percentage of the low boiling point liquid in the chilling liquidwithin the above indicated ranges the fragmentation number, or thedegree of toughening, may be adjusted as desired.

Generally, in order to obtain the same results, the smaller theexpansion coefficient of the glass, the higher must be the heat ofvaporization of the low boiling point liquid, or, at the same heat ofvaporization,

the concentration of low boiling point liquid must be higher.

The temperature of the quenching bath is significant, and is usuallymaintained at about, often just below, the 5 boiling point of the lowboiling point liquid. This ensures immediate boiling of the low boilingpoint liquid on the glass surface and very rapid heat extraction fromthe glass surfaces as the glass enters the chilling liquid.

10 Table V111 indicates the way in which variation of the bathtemperature can be seen to alter the degree of toughening of the glass.

In these experiments, 0.5% by weight of dichlorobenzene C H CI (Boilingpoint 180 C) were mixed with Shell Q.B.3 oil to constitute the chillingliquid.

TABLE Vlll Bath Temperature 100C 150C 200C.

Fragmentation 13 17 20 20 Number acetone 56 methanol 65 carbontetrachloride 76 1.1.1 trichlorocthane 74 1,2-dimethoxyethane 84 ethanol78 trichloroethcnc 87 4Q allyl isopropyl cthcne 83 allyl propyl ethene90 butyl ethenyl ether 94 diallyl ether 94 dipropyl ether 91 ethenylisobutyl ether 83 ethyl isobutyl ether 81 l-chloroethyl ether 722-chloroethyl ether 92 benzene 80 1-ch1oro-2 methoxybenzene 90 ethanephosphoric dimethylester 82 monochlorobenzene 132 dichlorobenzene 180chloroform 61 Heptane 98 Hexane 69 Octane 126 1,1 ,1,Z-tetrachloroethane 1 30 1,1 ,2,2-tetrachloroethane 146 1,1,2,trichloroethane 1 13 I 2-chloro-1-pheny1-ethano1 128 ternary butylalcohol 82 2,2-dichloroethanol 146 2dimethyl-amino ethanol 135 glycolmonoethyl ester 135 tetrachloroethene 121 butyl propyl ether 1 17S-methyl butyl ether 130 eyclohexyl methyl ether 133 dibutyl ether 1422chlorodiethyl ether 107 1,2-dichlorodiethy1 ether 140 2'-chloro ethenylether 108 1,2-dich1oroethenyl ether 128 5 ethyl hexyl ether 142 Toluenephosphorus oxychloride 105 phosphorus thiochloride phosphorus trimethylester 1 1 l isohutoxyctllanol 159 cthcnyl phcnyl cthcr 155Z-chIoro-toluene 159 3-chloro-toluenc 162 4-chloro-loluene 1622-butoxy-ethanol 171 benzyl methyl other 174 2,2-dichlorodiethyl ether178 benzyl chloride 179 When carrying out the method of the presentinvention on a large scale, such as for the mass production of glassesfor automobiles, it is advantageous to replenish continuously thevaporized low boiling point liquid.

This may be accomplished either by condensing the vapors of low boilingpoint liquid which rise from the quenching bath by indirect heatexchange, for instance by means of cooling coils and recycling thecondensed liquid into the quenching bath, or by the feeding of smallamounts of low boiling point liquid, for example continuouslydrop-by-drop, equivalent to the amounts thereof which have beenvaporized.

The rapid cooling of the hot glass which is achieved by the method ofthe present invention is based on the vaporization of the low boilingpoint liquid which is present in a relatively low concentration in thechilling liquid. The rapid withdrawal of heat from the glass by means ofthe liquid directly contacting the glass could also be carried out bydecomposition or chemical conversion of a liquid, and all energyconsuming processes in which the glass is rapidly cooled when it entersthe chilling liquid can be effective in producing the required degree oftoughening of the glass.

The vaporizing or decomposing cooling liquid is preferably continuouslyreplaced at such a rate that the concentration of low boiling pointliquid in the chilling liquid remains at least substantially constant.

Suitable combinations of high boiling point carrying liquid and lowboiling point liquid, the latter being present in an amount of up toabout 4% by weight of the chilling liquid, are set out in Table IX.

TABLE IX Carrying Liquid Low Boiling Point Liquid It will be apparentfrom Table IX that the low boiling point liquid is chosen to ensurefulfillment of the condition that the boiling point of the low boilingpoint liquid is 100 C or more below the incipient boiling point of thecarrying liquid.

Without further analysis, the foregoingwill so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

I claim:

1. Toughened glass which comprises a glass sheet having a thickness inthe range 0.8 mm to 3.5 mm, a modulus of rupture in the range 14 X 10p.s.i. to 56 X 10 p.s.i., and a fragmentation number upon destruction bysharp impact which is within the range of 8 fragments per cm tofragments per cm the fragments being characterised by granular naturefree of sharp edges.

2. Toughened glass which comprises a glass sheet of soda-lime-silicacomposition having a thickness in the range of 0.8 mm to 3.5 mm, amodulus of rupture in the range of 14 X 10 p.s.i. to 42 X 10 p.s.i., anda fragmentation number upon destruction by sharp impact which is withinthe range of 8 fragments per cm to 100 fragments per cm the fragmentsbeing characterised by granular nature free of sharp edges.

3. Toughened glass which comprises a sheet of glass of soda-lime-silicacomposition and having l) a thickness in the range of 0.8 mm to 3.5 mm,(2) a modulus of rupture in the range of 14 X 10" p.s.i. to 42 X 10p.s.i., and (3) a fragmentation number upon destruction by sharp impactwhich is within the range of 8 fragments per cm to 100 fragments per cm,the fragments being characterised by granular nature free of sharpedges.

4. For use in a vehicle windscreen, a sheet of glass of soda-lime-silicacomposition and having (1) a thickness in the range of 0.8 mm to 3.5 mm,(2) a modulus of rupture in the range of 14 X 10 p.s.i. to 56 X 10p.s.i., and (3) a fragmentation number upon destruction by sharp impactwhich is within the range of 8 fragments per cm to 100 fragments per cmthe fragments being characterised by granular nature free of sharpedges.

5. For use in a vehicle windscreen, a sheet of toughened glass ofsoda-lime-silica composition which sheet has a thickness in the range of0.8 mm to 3.5 mm, a modulus of rupture in the range 14 X 10 p.s.i. to 42X 10 p.s.i., and a fragmentation number upon destruction by sharp impactwhich is within the range of 8 fragments per cm to 100 fragments percm", the fragments being characterised by granular nature free of sharpedges.

6. Toughened glass comprising a sheet of glass of soda-lime-silicacomposition having a thickness within the range of 0.8 mm to 3.5 mm, amodulus of rupture within the range of 14 X 10 p.s.i. to 56 X 10 p.s.i.,a fragmentation number upon destruction by sharp impact which is withinthe range of 8 fragments per cm to 100 fragments per cm and having asubstantially continuous variation in stress therein, commencing withmaximum compressive stress at the glass surfaces and extending tomaximum tensile stress in the central region between the surfaces.

7. Toughened glass which comprises a glass sheet of soda-lime-silicacomposition having a thickness in the range 0.8 mm to 3.5 mm, a modulusof rupture within the range of 14 X 10 p.s.i. to 42 X 10 p.s.i., afragmentation number upon destruction by sharp impact which is withinthe range of 8 fragments per cm to 100 fragments per cm, and having asubstantially continuous variation in stress therein, commencing withmaximum compressive stress at the glass surfaces and extending tomaximum tensile stress in the central region between the surfaces.

8. Liquid quenched toughened glass of soda-limesilica of a thickness inthe range 1.5 mm to 2.5 mm, having a modulus of rupture in the range 14X p.s.i. to 42 X 10 p.s.i., and a fragmentation number upon destructionby sharp impact which is within the range of 8 fragments per cm to 75fragments per cm.

9. Toughened glass which comprises a glass sheet of soda-lime-silicacomposition having a thickness in the range 1.5 to 2.5 mm, a modulus ofrupture in the range 14 X 10 p.s.i. to 28 X 10 p.s.i., and afragmentation number upon destruction by sharp impact which is withinthe range of 8 fragments per cm to 65 fragments per cm the fragmentsbeing characterised by granular nature free of sharp edges.

10. Liquid quenched toughened glass of soda-limesilica compositionhaving (1) a thickness of 1.8 mm, (2) a modulus of rupture in the range14 X 10 p.s.i. to 56 X 10 p.s.i., and (3) a fragmentation number upondestruction by sharp impact which is within the range of 8 fragments percm to fragments per cm and having a substantially continuous variationin stress therein, commencing with maximum compressive stress at theglass surfaces and extending to maximum tensile stress in the centralregion between the surfaces.

1 l. Toughened glass which comprises a sheet of glass ofsoda-lime-silica composition having (1) a thickness of 1.8 mm (2) amodulus of rupture in the range 14 X 10 p.s.i. to 42 X 10 p.s.i., and(3) a fragmentation number upon destruction by sharp impact which iswithin the range of 8 fragments per cm to 75 fragments per cm thefragments being characterised by granular nature free of sharp edges.

12. Toughened glass which comprises a sheet of soda-lime-silica glass ofthickness 1.8 mm, having a modulus of rupture in the range 14 X 10p.s.i. to 28 X 10 p.s.i., and a fragmentation number upon destruction bysharp impact which is within the range 15 fragments per cm to 45fragments per cm the fragments being characterised by granular naturefree of sharp edges.

2. Toughened glass which comprises a glass sheet of soda-lime-silicacomposition having a thickness in the range of 0.8 mm to 3.5 mm, amodulus of rupture in the range of 14 X 103 p.s.i. to 42 X 103 p.s.i.,and a fragmentation number upon destruction by sharp impact which iswithin the range of 8 fragments per cm2 to 100 fragments per cm2, thefragments being characterised by granular nature free of sharp edges. 3.Toughened glass which comprises a sheet of glass of soda-lime-silicacomposition and having (1) a thickness in the range of 0.8 mm to 3.5 mm,(2) a modulus of rupture in the range of 14 X 103 p.s.i. to 42 X 103p.s.i., and (3) a fragmentation number upon destruction by sharp impactwhich is within the range of 8 fragments per cm2 to 100 fragments percm2, the fragments being characterised by granular nature free of sharpedges.
 4. For use in a vehicle windscreen, a sheet of glass ofsoda-lime-silica composition and having (1) a thickness in the range of0.8 mm to 3.5 mm, (2) a modulus of rupture in the range of 14 X 103p.s.i. to 56 X 103 p.s.i., and (3) a fragmentation number upondestruction by sharp impact which is within the range of 8 fragments percm2 to 100 fragments per cm2, the fragments being characterised bygranular nature free of sharp edges.
 5. For use in a vehicle windscreen,a sheet of toughened glass of soda-lime-silica composition which sheethas a thickness in the range of 0.8 mm to 3.5 mm, a modulus of rupturein the range 14 X 103 p.s.i. to 42 X 103 p.s.i., and a fragmentationnumber upon destruction by sharp impact which is within the range of 8fragments per cm2 to 100 fragments per cm2, the fragments beingcharacterised by granular nature free of sharp edges.
 6. Toughened glasscomprising a sheet of glass of soda-lime-silica composition having athickness within the range of 0.8 mm to 3.5 mm, a modulus of rupturewithin the range of 14 X 103 p.s.i. to 56 X 103 p.s.i., a fragmentationnumber upon destruction by sharp impact which is within the range of 8fragments per cm2 to 100 fragments per cm2, and having a substantiallycontinuous variation in stress therein, commencing with maximumcompressive stress at the glass surfaces and extending to maximumtensile stress in the central region between the surfaces.
 7. Toughenedglass which comprises a glass sheet of soda-lime-silica compositionhaving a thickness in the range 0.8 mm to 3.5 mm, a modulus of rupturewithin the range of 14 X 103 p.s.i. to 42 X 103 p.s.i., a fragmentationnumber upon destruction by sharp impact which is within the range of 8fragments per cm2 to 100 fragments per cm2, and having a substantiallycontinuous variation in stress therein, commencing with maximumcompressive stress at the glass sUrfaces and extending to maximumtensile stress in the central region between the surfaces.
 8. Liquidquenched toughened glass of soda-lime-silica of a thickness in the range1.5 mm to 2.5 mm, having a modulus of rupture in the range 14 X 103p.s.i. to 42 X 103 p.s.i., and a fragmentation number upon destructionby sharp impact which is within the range of 8 fragments per cm2 to 75fragments per cm2.
 9. Toughened glass which comprises a glass sheet ofsoda-lime-silica composition having a thickness in the range 1.5 to 2.5mm, a modulus of rupture in the range 14 X 103 p.s.i. to 28 X 103p.s.i., and a fragmentation number upon destruction by sharp impactwhich is within the range of 8 fragments per cm2 to 65 fragments percm2, the fragments being characterised by granular nature free of sharpedges.
 10. Liquid quenched toughened glass of soda-lime-silicacomposition having (1) a thickness of 1.8 mm, (2) a modulus of rupturein the range 14 X 103 p.s.i. to 56 X 103 p.s.i., and (3) a fragmentationnumber upon destruction by sharp impact which is within the range of 8fragments per cm2 to 75 fragments per cm2, and having a substantiallycontinuous variation in stress therein, commencing with maximumcompressive stress at the glass surfaces and extending to maximumtensile stress in the central region between the surfaces.
 11. Toughenedglass which comprises a sheet of glass of soda-lime-silica compositionhaving (1) a thickness of 1.8 mm (2) a modulus of rupture in the range14 X 103 p.s.i. to 42 X 103 p.s.i., and (3) a fragmentation number upondestruction by sharp impact which is within the range of 8 fragments percm2 to 75 fragments per cm2, the fragments being characterised bygranular nature free of sharp edges.
 12. Toughened glass which comprisesa sheet of soda-lime-silica glass of thickness 1.8 mm, having a modulusof rupture in the range 14 X 103 p.s.i. to 28 X 103 p.s.i., and afragmentation number upon destruction by sharp impact which is withinthe range 15 fragments per cm2 to 45 fragments per cm2, the fragmentsbeing characterised by granular nature free of sharp edges.